1. Field of the Invention
This description generally relates to the field of thermal printers, and more particularly to thermal printers that employ a portable power source, for example one or more batteries.
2. Description of the Related Art
Thermal printers produce a printed image by selectively forming a number of marks (e.g., dots) on a thermal paper or on other media via a thermal transfer ribbon. The marks are produced by a plurality of resistive elements of a thermal print head which heat the thermal paper or thermal ribbon to form successive lines. The lines ultimately form a desired image.
Existing battery operated thermal printers limit the number of resistive elements that are active at any given time to avoid overloading the power source (e.g., chemical battery) that powers such thermal printers. If the number of marks to be formed on a line exceeds the limit on the number of resistive elements that may be active at one time, then the resistive elements may be strobed in separate segments. However, strobing the resistive elements in segments may produce undesirable results. For example, such may cause steps in the lines due to movement of the media.
During use, the power source voltage may be reduced due to the electrical load of the thermal print head. A reduction in power source voltage may be compensated for by strobing the resistive elements of the print head for a longer time. Increasing the strobe time causes the resistive elements to emit more energy, thereby resulting in darker marks. However, increasing strobe time may cause the marks to be larger than otherwise desired. For example, some dots may have a larger diameter than other dots. Additionally, increasing strobe time reduces the speed at which the thermal printer operates. Reduced power source voltage may also disadvantageously limit the number of devices (e.g., resistive elements, motors and/or displays) that can be powered by the battery during use.
It is therefore desirable to have a new method and apparatus that addresses or alleviates at least some of the above stated problems.